Preliminary Analysis on Regeneration Effects of Gap Size in Two Coniferous Plantations

To clarify the effects of forest harvesting gap on the growth of 10 tree species planted and the regeneration of natural understory plants, 28 different size gaps (50-500 m²) were created and canopies were selected as controls in Pinus massoniana and Cunninghamia lanceolata plantations with identical habitats in Baiyun Mountain. The basal diameter and height of 10 tree species planted and understory plant diversity were investigated among the different forest gaps. The results show that (1) 10 tree species grew generally better in P. massoniana than in C. lanceolata plantation according to the comprehensive growth traits. Liquidambar formosana, Sapindus mukorossi, Sapium discolor and Altingia gracilipes grew better than the other tree species in P. massoniana plantation. L. formosana, S. discolor, Taxus chinensis var. mairei, S. mukorossi and A. gracilipes grew better than the others in C. lanceolata plantation. (2) The growth of T. chinensis var. mairei was significantly influenced by forest types, especially for the height (P < 0.01). The basal diameter and height of Schima superba were significantly influenced by gap size (P < 0.05). The interaction between forest type and gap size markedly affected the growth of tree species except for Celtis sinensis, Phoebe bournei and Phoebe chekiangensis. (3) The species richness, Simpson ecological dominance indices and Shannon diversity indices of natural understory plants differed significantly across the different size gaps (P < 0.05). These indices except for Simpson ecological dominance indices were significantly influenced by the plantation types (P < 0.05). The resembling coefficients of natural regeneration plants between the different size gaps were between 0.4 and 0.9 in two plantations. The resembling coefficients between the different size gaps were larger than that between in the gaps and at the control in the same plantation. The medium gaps with the size of 250 m² and the targeted tree species such as L. formosana, S. mukorossi, A. gracilipes and S. superba are recommended for broadleaved-oriented transformation of P. massoniana plantation. The large (500 m²) or small (50 m²) gaps and L. formosana, T. chinensis var. mairei, S. discolor, S. mukorossi and A. gracilipes are recommended for C. lanceolata plantation.